Fuse plug



Sept. 14, 1937. I I E, M Y 2,093,335

FqsE PLUG Filed June 11, 1936 thermal elementis shown engaged with Patented Sept. 14, 1937 PATENT OFFICE.

FUSE PLUG Charles m mag Application June 11,

4 Claims.

My invention relates to electric fuse plugs, more particularly having reference to devices of this character including a circuit breaker wherein the circuit may be broken by overload and re-set, permitting continued use of the plug.

In the art to which the invention relates fuse plugs, as well as other types of electric fuses, more usually employ a readily fusible element to break the circuit on overload, necessitating replacement of the plug which is both uneconomical and frequently inconvenient. The'present invention contemplates provision of a fuse plug in which the breaking of the circuit is a purely mechanical operation without injury to parts, permitting a new connection of the contact elements and continued use of the plug.

One of the objects of the invention is to provide an improved fuse plug of this character in which a thermal element is employed in the circult, said element being operative on overheating, as by overload or short circuit, to break the circuit, and being readily reconnectible to permit further use of the plug.-

A further object of the invention is to provide,

in conjunction with the thermal element, a movable contact member with which the thermal element is engageable, and including means for shifting the movable member out of engageable relation with the thermal element when disengagement has occurred.

A further object of the invention is to provide a device of this character that is of simple construction and operation, and economical to manufacture.

Other objects andadvantages of the invention will become apparent from the accompanying description talsen in conjunction with the drawing wherein like characters of reference indicate like parts throughout the several views, and wherein:

Fig. 1 shows a side view of a fuse plug of a character adapted for addition of my improvements, this being an open stock plug with certain minor changes.

Fig. 2 is a plan view of a fuse plug cap showing particularly the window through which the operative elements are insertable in the plug.

Fig. 3 is a sideview of a fuse plug embodying my improvements, the same being partly vertically sectioned and partly broken away to disclose the interior of the plug. In this view the the movable element.

Fig. 4 is a side view somewhat similar to that Wadena,- Saskatchewan, nada 1936, Serial No. 84,643

shown in Figure 3 but with the thermal element and movable contact in disengaged relation.

Fig. 5 is a perspective view of a relatively fixed contact member that forms the mounting for the movable contact member.

. Fig. 6 is a detail perspective view of the thermal element and bolt for its attachment.

Fig. 7 is a side view of the movable contact member taken by itself.

Having reference to the drawing the fuse plug, as in common use, includes a threaded metallic shell I, adapted to engage in a standard socket,

'the lower marginal portion of the shell being turned inward and engaged between insulating plates 2 and 3. The top of the shell is closed by a cap 4 which in the present showing is of a construction common in the art, including a window 5. I

The cap .4, for the purpose of the present invention, would include depending ears 6 at intervals around the marginal edge portion, said ears being adapted to be turned or crimped into engaging relation with a flanged edge I formed on the shell I. Between the ears 4 and edge I is inserted an annular insulating member 8.

Within the shell I is provided a terminal mounting 8 which provides depending legs lB-ll terminating in outwardly directed foot portions ll, engageable in the channel formed "by the thread of the shell, as is more readily apparent by reference to Figure 3. The mounting 9 is primarily adapted for convenient application of the invention for use with a fuse shell of the ordinary type in common use.

The mounting 9 constitutes a part of the one. terminal of the fuse plug and provides an upstanding portion bored for reception of a movable member II which forms a movable contact for the terminal and forms the terminal proper, it being understood a movable contact in a mounting forming an integral part of the shell could be provided in which case the contact would be designated as the terminal independent of its mounting.

To the member I3 is attached an insulating cap I by a screw l5. On the upstanding portion I2 is a spiral spring l6 tensioned to normally maintain the member If in an elevated position, the spring being engaged on stud ll. A bushing it of insulating materi provides protection for the spring against overheating.

The plates 2 and 3 are provided with a suitable opening for reception of a bolt I! which forms the center terminal for the plug. Said bolt engages the horizontal leg 20 of a thermal element 2|. The upper end of the element is turned down and back to form a catch member 22 engageable in an annular recess 28 formed in the movable contact is, said recess'deiining a head at with which the'member 22 may be engaged. The member 22 includes an attached contact point 22' of a metalhavlng a very high melting point, and which oiiers a minimum resistance to current and also wears well, for which purpose tantalum has been found very satisfactory.,

contact member It must be pushed down against the tension of spring 96. On release of the contact member thespring would elevate said member out of engaging relation with the catchmem= ber 22.

When the fuse plug isin use the catch member on the thermal element is engaged with the movable contact. An increase in temperature in excess of the proper carrying capacity of the thermal element, as by overload or short circuit,

would cause the vertical leg ofthe thermal element to move outwardly and disengage from the movable element 93 allowing said element to be displaced by the spring it out of engageable relation therewith. This engagement could .be re stored on cooling of the thermal element by depression of the member I3. I

The contacts are made of a terial not readily fusible when the arc occurs on disengagement. Metal has been found satisfactory for the movable contact.

The thermal element may be varied as to size to suit variations in load to be accommodated.

The essential elements constituting the circuit breaker could be readily adapted for use in the cartridge type of fuse .without departing from the principles of construction of the various eleaccuses To engage the member 22 with the head 26 the the advantages of the in 1.,A fuse plug includinga threaded shell adapted to engage in a standard socket, a terminal mounting carried by one end of the shell,

a movable contact slidable in said mounting, a fixed terminal in the other end of the shell, 2. thermal element attached to the fixed terminal, said movable contact having a head portion provided with an annular recess, and 'said thermal element including a catch member directly engageable with said recess, said catch member being disengageable therefrom on the thermal element being affected by an increase in tempcrature resulting from an excess of current, and

a spring mounted on the movable contact for' shifting said movable contact out of engageable relation with the thermal element on disengagement therefrom.

2. A device as defined in claim 1 wherein the terminal mounting is formed of a single piece of material bent; to provide depending legs with laterally projecting feet engageable in the threads of the shell, and including an upstanding portion bored for reception of the movable contact.

3. In a fuse plug including a shell terminal and a center terminal carried thereby at the one end, a movable terminal member carried by the other end of the shell, said member being mounted to be shiftable in relation to the center terminal, a thermal element attached to the center terminal, said element including ahead forming a catch member, and the movable terminal member providing a recess in which the catch membe'r is engageable, and a coiled spring on the movable terminal member, said spring being adapted to normally hold said member out of engageable relation with the catch-member on the thermal element.

. 4. Ida fuse plug including a shell terminal and a center terminal carried thereby at the one end and a thermal element attached to the center terminal, said element including a head forming a catch member, a movable terminal member carried by the other end of the shell, said member being mounted to be shiftable in relation tothe center terminal, and said member including a head with which the catch member on the thermal element is engageable, and spring means normally-holding the movable terminal member out of engageable relation with said catch member.

CHARLES EDGAR MOODY. 

